In the past few decades, the petroleum industry has invested heavily in the development of marine seismic survey techniques that yield knowledge of subterranean formations beneath a body of water in order to find and extract valuable mineral resources, such as oil. High-resolution seismic images of a subterranean formation are essential for quantitative seismic interpretation and improved reservoir monitoring. For a typical marine seismic survey, an exploration-seismology vessel tows one or more seismic sources and one or more streamers below the surface of the water and over a subterranean formation to be surveyed for mineral deposits. The vessel contains seismic acquisition equipment, such as navigation control, seismic source control, seismic receiver control, and recording equipment. The seismic source control causes the one or more seismic sources, which are typically air guns, to produce acoustic impulses at selected times. Each impulse is a sound wave that travels down through the water and into the subterranean formation. At each interface between different types of rock, a portion of the sound wave is refracted, a portion of the sound wave is transmitted, and another portion is reflected back toward the body of water to propagate toward the surface. The streamers towed behind the vessel are elongated cable-like structures. Each streamer includes a number of seismic receivers or sensors that detect pressure and/or particle motion changes in the water created by the sound waves reflected back into the water from the subterranean formation.
The sounds waves that propagate upwardly from the subterranean formation are referred to as “up-going” wavefields that are detected by the receivers and converted into seismic signals that are recorded by the recording equipment and processed to produce seismic images that characterize the geological structure and properties of the subterranean formation being surveyed. However, seismic signals may also include “source ghost” produced by sound waves that are first reflected from the sea surface before the waves travel into the subsurface to produce scattered wavefields detected by the receivers. Source ghosts are time delayed relative to sound waves that travel directly from the source to the subterranean formation. As a result, source ghosts can amplify some frequencies and attenuate other frequencies and are typically manifest as spectral notches in the recorded seismic waveforms, which make it difficult to obtain accurate high-resolution seismic images of the subterranean formation. In addition to the “source ghosts,” the seismic signal may also include “receiver ghosts” produced by scattered sound waves that are first reflected from the sea surface before reaching the receivers. The receiver ghosts can also amplify some frequencies and attenuate other frequencies and are typically manifested as receiver ghost notches. As a result, those working in the petroleum industry continue to seek systems and methods to remove the effects of ghost reflections, or “deghost” seismic signals.